1. Field of the Invention
The subject invention relates to femoral implants, and, more particularly, to a modular proximal femoral implant for replacing a femoral head and a method of implanting the same.
2. Description of the Invention Background
Hip replacements are common. A person""s hip joint may need to be replaced due to degeneration from severe trauma, such as an automobile accident, or from a plurality of etiologies, such as arthritis or disease. If the degeneration is severe, it may be necessary to replace the natural hip joint with a prosthetic hip. The femoral components of the hip joint are then replaced in whole or in part with a hip prosthesis. While hip implants are generally successful, they usually have to be replaced every few years because of the stress caused by the prosthesis.
A widely used design for replacement of the proximal portion of a femur employs an elongate, often curved, shaft that extends into the medullary canal of the femur. This design has the tendency to place unnatural stresses on the femur which lead to pain and the consequent curtailment of activity for the patient. The useful life of an intramedullary implant is often less than the expected life span of a young patient.
Previously known prostheses for replacing a femoral head that do not extend into the medullary canal have been mechanically complex or have proven troublesome in actual use. Huggler, U.S. Pat. No. 4,129,903 and Grimes, U.S. Pat. No. 4,795,473 are examples of prosthetic implants having a side plate attached to the exterior lateral side of the femur opposite the femoral head. Screws are used to secure the plate to the femur and one or more holes are drilled into the femur for securing the plate to the bone. The additional holes and the stresses at the site of fixation are believed to cause trauma to the bone.
Masini, U.S. Pat. No. 5,571,203 discloses a device having a shaft that extends through a resected portion of the proximal femur, positioned co-axially relative to the longitudinal axis of the femur. The device is secured by a screw or similar locking device that extends into the femur from the lateral side, just below the greater trochanter. It is believed that the natural forces applied to the prosthesis during normal hip motion result in the application of shear forces to the greater trochanter. The shear forces can be harmful to the greater trochanter and can permit micro-movement of the prosthesis on the unsecured side.
A conventional method for implanting the above types of femoral head implants is described in Campbell""s Operative Orthopaedics, (Mosby, 7th ed., 1987) and typically includes making a large incision in the patient""s lateral side at the hip joint and through the skin and muscle, dislocating the hip and then sawing off the femoral head. This method is considered invasive because of the need to dislocate the hip and cut through muscle surrounding the hip joint. Invasive procedures increase the trauma to the patient, the potential for complications, recovery time and the cost.
Replacement of the proximal portion of the femur is sometimes necessary due to degenerative bone disorders or trauma to otherwise healthy bone caused by accidental injury. In the latter instance it is desirable to replace the traumatized portion of the bone without causing further trauma to healthy bone. There is a need, therefore, for an implant that replaces a traumatized portion of the femur, but also significantly minimizes stress to the remaining healthy bone and that can be implanted by a method that is not invasive.
The present invention provides a proximal femoral replacement implant that both reduces trauma to the femur and the time required to perform the implantation. The design of the implant of the present invention transfers forces to the femur in a natural way and minimizes micromotion.
The implant of the present invention includes a body member having a longitudinal axis, a distal end and a proximal end. The body member is configured such that it is positioned in the natural femoral neck with passage of the distal end through the medial side of the femur, or through a reamer hole in the lateral side of the femur. The implant also includes a head member having a distal end and a proximal spherical portion configured for positioning in a natural or prosthetic hip socket, and a joining portion for joining the distal end of the head member to the proximal end of the body member. Furthermore, the implant includes a rod having a longitudinal axis, a distal end and a proximal end. The rod is configured such that it is positioned in the medullary (femoral) canal of the femur with passage through the body member in a direction transverse to the longitudinal axis of the body member.
The implant may also include a collar positioned at the proximal end of the body member and configured for abutting contact, in use, with a proximal surface of the resected femoral neck when the implant is inserted medially.
The body member is preferably configured in cross-section to inhibit rotational motion following implantation. The body member may be triangular, fluted or scalloped in cross-section. Alternatively, the body member may be circular in cross-section.
The body member and the head member may be integrally attached at the joining portion, but may also, and preferably, form modular components for complementary engagement with each other through joining portions. The joining portion preferably includes a first engagement portion and a second engagement portion, the first and second engagement portions being configured for complementary engagement with each other. The joining portion may extend outwardly from the body member at an acute angle relative to the longitudinal axis of the body member to provide anteversion. Alternatively, the joining portion may extend outwardly from the body member in substantial coaxial alignment with the longitudinal axis of the body member. The first engagement portion may be a recess formed either in the body member or the head member for receiving the second engagement portion and the second engagement portion may be a protrusion formed respectively, in the head member or the body member for insertion into the recess.
The modular embodiment of the implant of the present invention also preferably includes an optional member, preferably a sleeve, for altering the position of the spherical portion of the head member relative to the body member. The sleeve has an inner surface and an outer surface and defines a wall therebetween. It is mountable such that, in use, the inner surface slides over the protrusion and the outer surface is received within the recess. The sleeve may be longer in length than the protrusion of the joining portion for extending the distance between the spherical member and the body member. Additional sleeves may be provided wherein the wall has non-uniform, gradual thickness changes such that, in use, the central axis of the sleeve relative to the outer surface of the sleeve is at an acute angle to permit positioning of the head member at an angle relative to the longitudinal axis of the body member when needed.
The present invention further provides a method for implanting the proximal femoral replacement implant of the present invention using a reamer or burr which includes rotating the reamer into engagement with the lateral side of the femur and along the axis of the femoral neck to form a passage therethrough, morselizing the natural femoral head with the reamer or burr while keeping the natural femoral neck substantially intact, inserting the body member of the femoral replacement implant into the passage from the lateral side of the femur, forming another passage from the proximal end of the femur and into the medullary canal of the femur, and inserting a rod of the proximal femoral replacement implant from the proximal end of the femur through the body member and into the medullary canal of the femur.
Other details, objects and advantages of the present invention will become apparent with the following description of the present invention.